First direct evidence of cosmic inflation

17 March 2014

Almost 14 billion years ago, the universe we inhabit burst into existence in an extraordinary event that initiated the Big Bang. In the first fleeting fraction of a second, the universe expanded exponentially, stretching far beyond the view of our best telescopes. All this, of course, was just theory. Cardiff physicists are part of an international team that have turned this scientific theory into scientific fact.

Researchers from the BICEP2 collaboration today announced the first direct evidence for this cosmic inflation. Their data also represent the first images of gravitational waves, or ripples in space-time. These waves have been described as the "first tremors of the Big Bang." Finally, the data confirm a deep connection between quantum mechanics and general relativity.

"Detecting this signal is one of the most important goals in cosmology today. A lot of work by a lot of people has led up to this point," said John Kovac (Harvard-Smithsonian Center for Astrophysics), leader of the BICEP2 collaboration.

Professor Peter Ade of Cardiff University's School of Physics and Astronomy said "Having worked on many ground breaking CMB experiments for the last 30 years it is pleasing to finally confirm the inflationary hypothesis with this detection of B-modes." Dr Rashmi Sudiwala, a senior member of the Cardiff team, contributed to the experiment build and deployment in Antarctica, whilst Dr Carole Tucker contributed to the development and provision of key optical components.

These groundbreaking results came from observations by the BICEP2 telescope of the cosmic microwave background – a faint glow left over from the Big Bang. Tiny fluctuations in this afterglow provide clues to conditions in the early universe. For example, small differences in temperature across the sky show where parts of the universe were denser, eventually condensing into galaxies and galactic clusters.

Since the cosmic microwave background is a form of light, it exhibits all the properties of light, including polarization. On Earth, sunlight is scattered by the atmosphere and becomes polarized, which is why polarized sunglasses help reduce glare. In space, the cosmic microwave background was scattered by electrons and became polarized too.

"Our team hunted for a special type of polarization called 'B-modes,' which represents a twisting or 'curl' pattern in the polarized orientations of the ancient light," said co-leader Jamie Bock (Caltech/JPL).

Gravitational waves squeeze space as they travel, and have a "handedness," much like light waves, and can have left- and right-handed polarizations. It was predicted in the 1970s, by Cardiff University's Leonid Grishchuk, that this squeezing would produce a distinct pattern in the cosmic microwave background.

"The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky," said co-leader Chao-Lin Kuo (Stanford/SLAC).

The team examined spatial scales on the sky spanning about one to five degrees (two to ten times the width of the full Moon). To do this, they travelled to the South Pole to take advantage of its cold, dry, stable air.

"The South Pole is the closest you can get to space and still be on the ground," said Kovac. "It's one of the driest and clearest locations on Earth, perfect for observing the faint microwaves from the Big Bang."

They were surprised to detect a B-mode polarization signal considerably stronger than many cosmologists expected. The team analyzed their data for more than three years in an effort to rule out any errors. They also considered whether dust in our galaxy could produce the observed pattern, but the data suggest this is highly unlikely.

"This has been like looking for a needle in a haystack, but instead we found a crowbar," said co-leader Clem Pryke (University of Minnesota).

Professor Bangalore Sathyaprakash, a theoretical physicist at Cardiff University, commented that "This result is key to answering some of the biggest questions in cosmology. It provides insights into processes that took place in the early Universe, and just how violent the birth of the Universe was. It's wonderful to see the realisation of the prediction that our esteemed colleague Leonid Grishchuk made back in 1975"

"The next step in the story is to confirm this discovery with the Planck Satellite. The full analysis of the Planck data is currently ongoing, and we hope will be ready for release later this year", concluded Professor Ade.